Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.[7] It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica)

I want to come back to this in a second, but here is a story the Bryan Caplan posted on his blog. He is quoting from Tetlock and Gardner's Superforecasting

In March 1951 National Intelligence Estimate (NIE) 29-51 was published. "Although it is impossible to determine which course of action the Kremlin is likely to adopt," the report concluded, "we believe that the extent of [Eastern European] military and propaganda preparations indicate that an attack on Yugoslavia in 1951 should be considered a serious possibility." ...But a few days later, [Sherman] Kent was chatting with a senior State Department official who casually asked, "By the way, what did you people mean by the expression 'serious possibility'? What kind of odds did you have in mind?" Kent said he was pessimistic. He felt the odds were about 65 to 35 in favor of an attack. The official was started. He and his colleagues had taken "serious possibility" to mean much lower odds.

Disturbed, Kent went back to his team. They had all agreed to use "serious possibility" in the NIE so Kent asked each person, in turn, what he thought it meant. One analyst said it meant odds of about 80 to 20, or four times more likely than not that there would be an invasion. Another thought it meant odds of 20 to 80 - exactly the opposite. Other answers were scattered between these extremes. Kent was floored.

Let's go back to the IPCC summary conclusion, which is quoted and used all over the place (no one in the media ever actually digs into the charts and analysis, they just stop at this quote). A few thoughts:

This kind of conclusion is typical of team process and perhaps is a reason that large teams shouldn't do scientific studies. We wouldn't have aspirin if 500 people all had to agree on a recommendation to allow it.

Climate alarmists often claim "consensus". Part of the way they get consensus is by excluding anyone who disagrees with them from the IPCC process and publication. But even within the remaining core, scientists have vast differences in how they evaluate the data. Consensus only exists because the conclusions use weasel words with uncertain meaning like "most" and "significant" (rather than a percentage) and "very likely" (rather than a probability).

Is "most" 51% or 95%? The difference between these two is almost a doubling of the implied temperature sensitivity to CO2 -- close to the magnitude of difference between lukewarmer and IPCC estimates. Many skeptics (including myself) think past warming due to man might be 0.3-0.4C which is very nearly encompassed by "most".

It may be that this uncertainty is treated as a feature, not a bug, by activists, who can take a word scientists meant to mean 51% and portray it as meaning nearly 100%.

For an example of this sort of thing taken to an extreme, arguably corrupt level, consider the original 97% global warming consensus survey which asked 77 scientists hand-selected from a pool of over 10,000 working on climate-related topics two questions. Answering yes to the two questions put you in the 97%. In the context of what was written above, note the wording:

That anything-but-scientific survey asked two questions. The first: “When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?” Few would be expected to dispute this…the planet began thawing out of the “Little Ice Age” in the middle 19th century, predating the Industrial Revolution. (That was the coldest period since the last real Ice Age ended roughly 10,000 years ago.)

The second question asked: “Do you think human activity is a significant contributing factor in changing mean global temperatures?” So what constitutes “significant”? Does “changing” include both cooling and warming… and for both “better” and “worse”? And which contributions…does this include land use changes, such as agriculture and deforestation?

Good Lord, I am a hated skeptic frequently derided as a denier and I would answer both "yes" and be in the 97% consensus. So would most all of the prominent science-based skeptics you have ever heard of.

Believe it or not, I am not going to update on the CRU emails. The insights into the science process are illuminating, and confirm much that we have suspected, but faults in transparency do not automatically win the game -- they lead to [hopefully] future transparency which then allows for better criticism and/or replication of the work.

My frustration today is a recent article in Scientific American [with the lofty academic title "Seven Answers to Climate Contrarian Nonsense"] which purports to shoot down the seven key skeptics arguments. Many others have shown how the author does not do a very good job of shooting down these seven, but that is not my main frustration. The problem is that, like many of the global warming myth buster articles like this, the author completely fails to address the best, core arguments of skeptics, preferring to snipe around at easier prey at the margins.

Here are my seven alternative skeptics' claims I would like to see addressed:

Claim A: Nearly every scientist, skeptic and alarmist alike, agree that the first order warming from CO2 is small. Catastrophic forecasts that demand immediate government action are based on a second theory that the climate temperature system is dominated by positive feedback. There is little understanding of these feedbacks, at least in their net effect, and no basis for assuming feedbacks in a long-term stable system are strongly net positive. As a note, the claim is that the net feedbacks are not positive, so demonstration of single one-off positive feedbacks, like ice albedo, are not sufficient to disprove this claim. In particular, the role of the water cycle and cloud formation are very much in dispute.

Claim B: At no point have climate scientists ever reconciled the claims of the dendroclimatologists like Michael Mann that world temperatures were incredibly stable for thousands of years before man burned fossil fuels with the claim that the climate system is driven by very high net positive feedbacks. There is nothing in the feedback assumptions that applies uniquely to CO2 forcing, so these feedbacks, if they exist today, should have existed in the past and almost certainly have made temperatures highly variable, if not unstable.

Claim C: On its face, the climate model assumptions (including high positive feedbacks) of substantial warming from small changes in CO2 are inconsistent with relatively modest past warming. Scientists use what is essentially an arbitrary plug variable to handle this, assuming anthropogenic aerosols have historically masked what would be higher past warming levels. The arbitrariness of the plug is obvious given that most models include a cooling effect of aerosols in direct proportion to their warming effect from CO2, two phenomenon that should not be linked in nature, but are linked if modelers are trying to force their climate models to balance. Further, since aerosols are short lived and only cover about 10% of the globe's surface in any volume, nearly heroic levels of cooling effects must be assumed, since it takes 10C of cooling from the 10% area of effect to get 1C cooling in the global averages.

Claim D: The key issue is the effect of CO2 vs. other effects in the complex climate system. We know CO2 causes some warming in a lab, but how much on the real earth? The main evidence climate scientists have is that their climate models are unable to replicate the warming from 1975-1998 without the use of man-made CO2 -- in other words, they claim their models are unable to replicate the warming with natural factors alone. But these models are not anywhere near good enough to be relied on for this conclusion, particularly since they admittedly leave out any number of natural factors, such as ocean cycles and longer term cycles like the one that drove the little ice age, and admit to not understanding many others, such as cloud formation.

Claim E: There are multiple alternate explanations for the 1975-1998 warming other than manmade CO2. All likely contributed (along with CO2) but it there is no evidence to give most of the blame to Co2. Other factors include ocean cycles (this corresponded to a PDO warm phase), the sun (this corresponded to the most intense period of the sun in the last 100 years), mankind's land use changes (driving both urban heating effects as well as rural changes with alterations in land use), and a continuing recovery from the Little Ice Age, perhaps the coldest period in the last 5000 years.

Claim F: Climate scientists claim that the .4-.5C warming from 1975-1998 cannot have been caused natural variations. This has never been reconciled with the fact that the 0.6C warming from 1910 to 1940 was almost certainly due mostly to natural forces. Also, the claim that natural forcings could not have caused a 0.2C per decade warming in the 80's and 90's cannot be reconciled with the the current claimed natural "masking" of anthropogenic warming that must be on the order of 0.2C per decade.

Claim G: Climate scientists are embarrassing themselves in the use of the word "climate change." First, the only mechanism ever expressed for CO2 to change climate is via warming. If there is no warming, then CO2 can't be causing climate change by any mechanism anyone has ever suggested. So saying that "climate change is accelerating" (just Google it) when warming has stopped is disingenuous, and a false marketing effort to try to keep the alarm ringing. Second, the attempts by scientists who should know better to identify weather events at the tails of the normal distribution and claim that these are evidence of a shift in the mean of the distribution is ridiculous. There are no long term US trends in droughts or wet weather, nor in global cyclonic activity, nor in US tornadoes. But every drought, hurricane, flood, or tornado is cited as evidence of accelerating climate change (see my ppt slide deck for the data). This is absurd.

Al Gore says that current global temperatures are the highest they have been in 1000 years. A new study by the Institute of Astronomy in Zurich says that the "sun is more active now than it has been at anytime in the previous 1,000 years." Related?

Sunspots have been monitored on the Sun since 1610,
shortly after the invention of the telescope. They provide the
longest-running direct measurement of our star's activity.

The variation in sunspot numbers has revealed the Sun's 11-year cycle of activity as well as other, longer-term changes.

In particular, it has been noted that between about 1645 and 1715, few sunspots were seen on the Sun's surface.

This period is called the Maunder Minimum after the English astronomer who studied it.

It coincided with a spell of prolonged cold weather
often referred to as the "Little Ice Age". Solar scientists strongly
suspect there is a link between the two events - but the exact
mechanism remains elusive....

But the most striking feature, he says, is that
looking at the past 1,150 years the Sun has never been as active as it
has been during the past 60 years.

Over the past few hundred years, there has been a steady
increase in the numbers of sunspots, a trend that has accelerated in
the past century, just at the time when the Earth has been getting
warmer.

The data suggests that changing solar activity is influencing in some way the global climate causing the world to get warmer.

Of course, these poor scientists know that they could lose their jobs and be called Holocaust deniers if they don't acknowledge anthropomorphic global warming, so they do say:

Over the past 20 years, however, the number of
sunspots has remained roughly constant, yet the average temperature of
the Earth has continued to increase.

This is put down to a human-produced greenhouse effect caused by the combustion of fossil fuels. (HT: TJIC)

Which may actually be the case, but it is interesting that astronomers feel the need to say this without any evidence of such in their own study just to protect themselves from ostracism by the climate religionists.

However, even if the two are working in concert, the fact that solar activity explains some of the 20th century warming means that current climate models are WAY overestimating the impact of anthropomorphic warming.

For example, the climate models in the current 2007 IPCC report assume that the world would have experienced no warming in the 20th century without man. This is from Section 8, actual is the black line, the models without man are in blue, the models with man are in red:

In other words, the IPCC models completely ignore the increasing solar activity and assume 100% of 20th century warming was due to man-made effects, even the substantial warming before 1940 (and before the onset of truly heavy world-wide fossil fuel use).

Already, the models used by the IPCC tend to overestimate past warming even if all past warming is attributable to anthropomorphic causes. If anthropomorphic effects explain only a fraction of past warming, then the current models are vastly overstated, good for stampeding the populous into otherwise unpopular political control over the economy, but of diminished scientific value.

Postscript: I cannot prove this, but I am willing to make a bet based on my long, long history of modeling (computers, not fashion). My guess is that the blue band, representing climate without man-made effects, was not based on any real science but was instead a plug. In other words, they took their models and actual temperatures and then said "what would the climate without man have to look like for our models to be correct." There are at least four reasons I strongly suspect this to be true:

Every computer modeler in history has tried this trick to make their models of the future seem more credible. I don't think the climate guys are immune.

There is no way their models, with our current state of knowledge about the climate, match reality that well.

The first time they ran their models vs. history, they did not match at all. This current close match is the result of a bunch of tweaking that has little impact on the model's predictive ability but forces it to match history better. For example, early runs had the forecast run right up from the 1940 peak to temperatures way above what we see today.

The blue line totally ignores any of our other understandings about the changing climate, including the changing intensity of the sun. It is conveniently exactly what is necessary to make the pink line match history. In fact, against all evidence, note the blue band falls over the century. This is because the models were pushing the temperature up faster than we have seen it rise historically, so the modelers needed a negative plug to make the numbers look nice.